Hairy regulars upset first man describing fleet (6)
I believe the answer is:
armada
'fleet' is the definition.
(I know that armada is a type of fleet)
'hairy regulars upset first man' is the wordplay.
'regulars' indicates alternate letters (letters selected at regular intervals).
'upset' is a reversal indicator.
'first man' becomes 'adam' (first man in the Bible).
The alternate letters of 'hairy' are 'ar'.
'adam' back-to-front is 'mada'.
'ar'+'mada'='ARMADA'
'describing' is the link.
(Other definitions for armada that I've seen before include "sea-borne unit" , "Spanish war fleet" , "Old Spanish fleet" , "Large number of ships (Spanish?)" , "The Spanish force" .)